Environmental groups asked a federal court Tuesday to halt a PSEG project that will upgrade an electrical transmission line through the Delaware Water Gap National Recreation Area and bring more energy capacity to North Jersey.

The groups said the court should halt construction until it rules on the environmentalists’ pending suit opposing the project, because otherwise the construction work would do irreparable harm to the scenic vistas in the Delaware Water Gap area.

The project “will permanently scar the landscape and damage unique geological and ecological resources in three treasured national park units,” the environmental groups argue in their motion, filed in United State District Court for the District of Columbia.

In their original suit, filed last year, the New Jersey chapter of the Sierra Club and other groups argue that the National Park Service did not follow various federal environmental laws when it reviewed and ultimately approved PSEG’s project through the national recreation area.

The project involves upgrading 45 miles of transmission lines through environmentally sensitive land in the New Jersey Highlands, following the existing right of way of the 230,000-volt Susquehanna-Roseland transmission line. The $750-million project is adding a 500,000-volt line to the existing line, and replacing about 240 support towers that are 72 to 187 feet tall with larger lattice and monopoles that are 145 to 195 feet tall.

PSEG had originally applied for project approval in 2009, and the state Board of Public Utilities signed off the next year, saying that without it, system overloads could cause “significant damage to infrastructure, brownouts or blackouts.”

The environmental groups had tried to stop the project with a similar suit at the state level, but a New Jersey Superior Court said in February that it found “sufficient credible evidence” that the upgrade was designed to improve the region’s electric grid infrastructure.

Since then, PSEG has already finished upgrading about 26 miles worth of the project route, said George Sous, PSEG’s manager of state transmission outreach.

The company plans to start work on the Delaware Water Gap phase of the project Sept. 3 by building 3.5 miles of new 20-foot wide access roads and clearing 4.6 acres of mature trees. By Oct. 1, it is scheduled to place foundations for 26 transmission towers along a 4.3-mile right of way.

PSEG’s Sous said that an injunction, even for a few months, could cause a delay of as much as a year in construction, given that the company can only take sections of the existing line out of commission to make the improvements during the fall and winter months, when energy demand is not at its peak.

The Sierra Club’s Jeff Tittel said PSEG should have routed the new line around the Delaware Water Gap area. But Sous said that even if the company had done so, the original transmission line and towers would have remained in the natural area, while the route for the new 500,000-volt line would have caused disruption to property owners and previously undisturbed environmentally sensitive land.

Sous also said that the original line was constructed in the 1920s, long before the area had come under the oversight of the National Park Service.

“It’s critical this major line gets upgraded as soon as possible. We need to bring more energy into North Jersey,” Sous said. “PSEG is significantly committed to the environment, and we feel this necessary project can and will be done responsibly.”

Environmental groups asked a federal court Tuesday to halt a PSEG project that will upgrade an electrical transmission line through the Delaware Water Gap National Recreation Area and bring more energy capacity to North Jersey.

The groups said the court should halt construction until it rules on the environmentalists’ pending suit opposing the project, because otherwise the construction work would do irreparable harm to the scenic vistas in the Delaware Water Gap area.

The project “will permanently scar the landscape and damage unique geological and ecological resources in three treasured national park units,” the environmental groups argue in their motion, filed in United State District Court for the District of Columbia.

In their original suit, filed last year, the New Jersey chapter of the Sierra Club and other groups argue that the National Park Service did not follow various federal environmental laws when it reviewed and ultimately approved PSEG’s project through the national recreation area.

The project involves upgrading 45 miles of transmission lines through environmentally sensitive land in the New Jersey Highlands, following the existing right of way of the 230,000-volt Susquehanna-Roseland transmission line. The $750-million project is adding a 500,000-volt line to the existing line, and replacing about 240 support towers that are 72 to 187 feet tall with larger lattice and monopoles that are 145 to 195 feet tall.

PSEG had originally applied for project approval in 2009, and the state Board of Public Utilities signed off the next year, saying that without it, system overloads could cause “significant damage to infrastructure, brownouts or blackouts.”

The environmental groups had tried to stop the project with a similar suit at the state level, but a New Jersey Superior Court said in February that it found “sufficient credible evidence” that the upgrade was designed to improve the region’s electric grid infrastructure.

Since then, PSEG has already finished upgrading about 26 miles worth of the project route, said George Sous, PSEG’s manager of state transmission outreach.

The company plans to start work on the Delaware Water Gap phase of the project Sept. 3 by building 3.5 miles of new 20-foot wide access roads and clearing 4.6 acres of mature trees. By Oct. 1, it is scheduled to place foundations for 26 transmission towers along a 4.3-mile right of way.

PSEG’s Sous said that an injunction, even for a few months, could cause a delay of as much as a year in construction, given that the company can only take sections of the existing line out of commission to make the improvements during the fall and winter months, when energy demand is not at its peak.

The Sierra Club’s Jeff Tittel said PSEG should have routed the new line around the Delaware Water Gap area. But Sous said that even if the company had done so, the original transmission line and towers would have remained in the natural area, while the route for the new 500,000-volt line would have caused disruption to property owners and previously undisturbed environmentally sensitive land.

Sous also said that the original line was constructed in the 1920s, long before the area had come under the oversight of the National Park Service.

“It’s critical this major line gets upgraded as soon as possible. We need to bring more energy into North Jersey,” Sous said. “PSEG is significantly committed to the environment, and we feel this necessary project can and will be done responsibly.”